Old Scared Ponies
I actually have not seen or worked with these two ponies in a long time, but I was thinking about them just now and I'm curious to see what other people think. This is the perfect case of "hindsight is 20/20."
At a stable I previously worked at, we had two 20+ year old ponies that were full siblings and were used for driving, either alone or as a pair. The stable owner had owned them their entire lives, raised and trained them herself. They never spooked at anything while driving. However, they were incredibly spooky when ridden or handled on the ground. I rode them a handful of times and anything as quiet and little as adjusting your arm and your jacket brushing against itself would send them off in a bolting panic before they realized it was ridiculous and stop and walk on like it never happened.
In particular, they hated blanket removal. The owner had a policy that all horses kept their chest buckles fastened and you would remove the blanket by sliding the whole thing up their neck and off their heads. Don't ask me why she insisted on this, it's a whole discussion in itself. Every time they had a blanket removed, and I mean every single time, without fail, these two ponies would fly backwards out of the blanket and look at you wide-eyed and shaky-kneed. Putting the blankets back on in the reverse manner (blanket over the head and slide down the neck) didn't phase them. All the other horses (75% of which were also raised and trained by this lady) had absolutely no issue with this method of blanket removal.
You'd think, even without deliberate desensitizing, that they would have eventually grown accustomed to it after over twenty years of twice-daily blanket changes for about half of each year. The owner told me that they've just always been incredibly spooky compared to her other born-and-raised-here horses, and for years she's made deliberate attempts through many methods to train them out of spookiness with no avail. The two ponies were entirely unrelated to the other horses she had bred. Is this just a trait that's resulted from their breeding? Were they just especially prone to spooking at things happening behind their line of sight that would typically be shielded by blinds while driving? Of course, I don't exactly need advice since I don't work there anymore, but I'm just more curious as to what you think was going on.